Truck cab bumper unit exterior surface



FIG. 1 is a side elevation view of a truck cab bumper unit exterior surface showing my new design, it being understood that the broken lines are for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a perspective view thereof; and 

The ornamental design for a truck cab bumper unit exterior surface, as shown and described. 